Enhanced biological nitrogen removal in MLE combined with post-denitrification process and EF clarifier

Abstract

A modified ludzack ettinger reactor (MLE) combined with a post-denitrification reactor (PDMLE) using electroflotation (EF) as a secondary clarifier was investigated on its feasibility and process performance. Results indicated that higher mixed liquor suspended solids (MLSS) concentrations in bioreactor (5,350 +/- A 352 mg L-1) were maintained via the highly concentrated return sludge (16,771 +/- A 991 mg L-1) from the EF clarifier and the effluent suspended solids (SS) concentrations continued relatively low, representing effluent SS concentration of 1.71 +/- A 1.16 mg L-1, compared with GS-A2O process during the operation of four months. The denitrification was improved by combining MLE process with post-denitrification based on endogenous decay (i.e. no additional carbon source was added), resulting in the removal efficiencies of TN were about 91 and 59% for the influent C/N ratio of 10 and 5, respectively, revealing relatively high nitrogen removal as compared with EF-A2O and gravity settling (GS)-A2O processes as a control. The nitrogen balance analysis indicates that pre-denitrification and post-denitrification contributed to 78 and 22% of TN removed, respectively.